U.S. Pat. No. 4,261,545 owned by Sloan Valve Company of Franklin Park, Ill., assignee of the present application discloses a flush valve which is sold by that company under the trademark "GEM". There is a piston which opens and closes the flush valve, with the piston normally being maintained in a closed position by water pressure at the inlet. Inlet pressure is applied to a piston chamber through a small orifice in the wall of the piston. There is a relief valve which is used to vent the piston chamber permitting the piston to move away from its valve seat and to thus open the valve.
In the flush valve shown in the '545 patent the cover is sealed to the body by means of a two-ring peripheral seal. One of the two rings is a slip ring and the other is a gasket. As the cover is turned down it slides upon the upper surface of the slip ring which then applies distorting pressure to the gasket. The slip ring is necessary, as otherwise if the cover is turned down directly upon the gasket, the surface of the gasket would be torn and the seal would be lost.
The present invention provides a single seal member which performs both of the functions of the prior art slip ring and gasket. This single seal element has a surface finish which provides the required lubricity for the cover to slide upon its surface. The seal element also has the necessary elastomeric and distortion characteristics so as to form a tight seal between the cover and the body.
The single element seal of the present invention not only provides the desired sealing characteristics, but eliminates one of the two parts required in prior seal constructions. The elimination of a part is important, as often in assembly of the valve, either in the field or prior to shipment, one of the two parts could be inadvertently damaged or misplaced. By having a single part perform a dual function, there is not only a part and labor cost saving, but also insurance that the valve will be shipped and assembled in a workable manner.
Further, in the prior art seal construction such as shown in the '545 patent, the gasket was placed in a pocket with the result that the normal mushrooming of a distortable element forced the gasket against the side walls of the body. This may be advantageous if the elements are assembled in the correct alignment, but can cause a leaky valve if the sealing elements are mounted contrary to assembly specifications. The use of the single seal element of the present invention does not require a specific assembly process and can in fact be installed with either side facing down or up, an essentially error-free installation process.